Changes In Speech Intelligibility Research Articles

Dissociated neural tracking as an index of speech understanding in background noise

Human brain activity has been shown to track hierarchical linguistic units embedded in connected speech and these responses can be directly modulated by changes in speech intelligibility caused by spectral degradation or prior knowledge. In this study, we introduce a background noise and manipulate its level relative to the target speech to test the hypothesis that the tracking responses are modulated differently by the variations in Signal-to-Noise Ratio (SNR) and changes in speech intelligibility. Electroencephalography (EEG) responses to speech in quiet and in noise (multi-talker babble) at three different levels were measured from 19 normal hearing participants. Driven by the reduction in intelligibility, cortical coherence to “abstract” linguistic units with no accompanying acoustic cues was reduced relative to the “speech only” condition, and lateralized to single cerebral hemispheres. In contrast, brain responses coherent to words, aligned with acoustic onsets, were bilateral and reduced systematically as noise level increased. Strength of the tracking response correlated with subjective ratings from each participant on how much they can understand the speech sentences at all different linguistic levels. These results provide an objective and sensitive neural marker of speech intelligibility which can be further developed into clinical applications for objective assessment of speech-in-noise understanding.

Naive Listener Ratings of Speech Intelligibility Over the Course of Motor-Based Intervention in Children With Childhood Apraxia of Speech.

The aim of this study was to describe changes in speech intelligibility and interrater and intrarater reliability of naive listeners' ratings of words produced by young children diagnosed with childhood apraxia of speech (CAS) over a period of motor-based intervention (dynamic temporal and tactile cueing [DTTC]). A total of 120 naive listeners (i.e., listeners without experience listening to children with speech and/or language impairments; age range: 18-45 years) orthographically transcribed single-word productions by five children (age range: 2;6-3;11 [years;months]) across three time points over an intervention period (baseline, post-treatment, maintenance). Changes in intelligibility and interrater and intrarater reliability were examined within and across time points. Speech intelligibility significantly increased in children with CAS over the course of treatment, and these gains were also maintained at 6 weeks posttreatment. There was poor-to-fair consistency between listeners (interrater reliability) and excellent consistency within listeners (intrarater reliability) in ratings of speech intelligibility within and across time points. Motor-based intervention increases speech intelligibility following a period of DTTC treatment. Variability among naive listeners of speech intelligibility was also present, with intrarater reliability (within listeners) yielding greater consistency than interrater reliability (between listeners). The implications for including naive listeners as raters of speech intelligibility for research and clinical purposes are discussed.

The effects of speech masking on neural tracking of acoustic and semantic features of natural speech

Listening environments contain background sounds that mask speech and lead to communication challenges. Sensitivity to slow acoustic fluctuations in speech can help segregate speech from background noise. Semantic context can also facilitate speech perception in noise, for example, by enabling prediction of upcoming words. However, not much is known about how different degrees of background masking affect the neural processing of acoustic and semantic features during naturalistic speech listening. In the current electroencephalography (EEG) study, participants listened to engaging, spoken stories masked at different levels of multi-talker babble to investigate how neural activity in response to acoustic and semantic features changes with acoustic challenges, and how such effects relate to speech intelligibility. The pattern of neural response amplitudes associated with both acoustic and semantic speech features across masking levels was U-shaped, such that amplitudes were largest for moderate masking levels. This U-shape may be due to increased attentional focus when speech comprehension is challenging, but manageable. The latency of the neural responses increased linearly with increasing background masking, and neural latency change associated with acoustic processing most closely mirrored the changes in speech intelligibility. Finally, tracking responses related to semantic dissimilarity remained robust until severe speech masking (−3 dB SNR). The current study reveals that neural responses to acoustic features are highly sensitive to background masking and decreasing speech intelligibility, whereas neural responses to semantic features are relatively robust, suggesting that individuals track the meaning of the story well even in moderate background sound.

Delta-band neural envelope tracking predicts speech intelligibility in noise in preschoolers

Behavioral tests are currently the gold standard in measuring speech intelligibility. However, these tests can be difficult to administer in young children due to factors such as motivation, linguistic knowledge and cognitive skills. It has been shown that measures of neural envelope tracking can be used to predict speech intelligibility and overcome these issues. However, its potential as an objective measure for speech intelligibility in noise remains to be investigated in preschool children. Here, we evaluated neural envelope tracking as a function of signal-to-noise ratio (SNR) in 14 5-year-old children. We examined EEG responses to natural, continuous speech presented at different SNRs ranging from −8 (very difficult) to 8 dB SNR (very easy). As expected delta band (0.5-4 Hz) tracking increased with increasing stimulus SNR. However, this increase was not strictly monotonic as neural tracking reached a plateau between 0 and 4 dB SNR, similarly to the behavioral speech intelligibility outcomes. These findings indicate that neural tracking in the delta band remains stable, as long as the acoustical degradation of the speech signal does not reflect significant changes in speech intelligibility. Theta band tracking (4-8 Hz), on the other hand, was found to be drastically reduced and more easily affected by noise in children, making it less reliable as a measure of speech intelligibility. By contrast, neural envelope tracking in the delta band was directly associated with behavioral measures of speech intelligibility. This suggests that neural envelope tracking in the delta band is a valuable tool for evaluating speech-in-noise intelligibility in preschoolers, highlighting its potential as an objective measure of speech in difficult-to-test populations.

Oral Incompetence: changes in speech intelligibility following facial nerve paralysis

BackgroundSpeech may be compromised following facial nerve paralysis (FNP), depending on the cause of the paralysis. This can result in lower quality of life and a reduced capacity to return to vocational roles. Despite its prevalence, it is incompletely understood and rarely described. This study prospectively evaluated the impact of FNP on speech intelligibility. MethodsThis observational study recruited patients who were diagnosed with FNP and who reported oral incompetence from the Sydney Facial Nerve Service. Their speech was analysed using patient reported outcome measures (Speech Handicap Index) and perceived intelligibility (Speech Pathologist, community member control participants, participant self-rating, and dictation software). ResultsForty participants with FNP and 40 controls were recruited. Participants with FNP rated their intelligibility to be significantly worse than other raters (p <0.001). Consonant analysis demonstrated bilabial, fricatives and labiodental phonemes to be most commonly affected following FNP. ConclusionOral competence is compromised after FNP which can lead to a poorer perception of their intelligibility and reduced speech related quality of life.

Variation in Speech Intelligibility Ratings as a Function of Speech Rate Modification in Parkinson's Disease.

Purpose The aim of this study was to quantify changes in speech intelligibility in two cohorts of people with Parkinson's disease (PD; those with and without deep brain stimulation [DBS]) across a broad range of self-selected speech rate alterations in (a) read sentences and (b) extemporaneous speech (monologues). Method Four speaker groups participated in this study: younger and older controls, people with PD undergoing standard pharmaceutical treatment, and people with PD and DBS. Naïve listeners rated the intelligibility of read sentences and extemporaneous monologues, spoken by participants at seven self-selected speech rates from very slow to very fast. Intelligibility was modeled as a function of group, speech rate condition, and speech task. Results Overall, compared to habitual speech rate, slower speech rate conditions were not associated with changes in speech intelligibility, whereas faster-than-habitual conditions were associated in declines in intelligibility. Results were mediated by group and task effects, such that talkers with PD and DBS were more likely to see intelligibility benefits at slower self-selected speech rates and less likely to see detriments at faster rates, and these differences were amplified in monologues compared to sentences. Conclusion Findings suggest differences in the ways in which slower and faster speech rate adjustments impact speech intelligibility in people with PD with and without DBS, with the latter demonstrating greater magnitudes of change.

Lateralized Cerebral Processing of Abstract Linguistic Structure in Clear and Degraded Speech.

Human cortical activity measured with magnetoencephalography (MEG) has been shown to track the temporal regularity of linguistic information in connected speech. In the current study, we investigate the underlying neural sources of these responses and test the hypothesis that they can be directly modulated by changes in speech intelligibility. MEG responses were measured to natural and spectrally degraded (noise-vocoded) speech in 19 normal hearing participants. Results showed that cortical coherence to "abstract" linguistic units with no accompanying acoustic cues (phrases and sentences) were lateralized to the left hemisphere and changed parametrically with intelligibility of speech. In contrast, responses coherent to words/syllables accompanied by acoustic onsets were bilateral and insensitive to intelligibility changes. This dissociation suggests that cerebral responses to linguistic information are directly affected by intelligibility but also powerfully shaped by physical cues in speech. This explains why previous studies have reported widely inconsistent effects of speech intelligibility on cortical entrainment and, within a single experiment, provided clear support for conclusions about language lateralization derived from a large number of separately conducted neuroimaging studies. Since noise-vocoded speech resembles the signals provided by a cochlear implant device, the current methodology has potential clinical utility for assessment of cochlear implant performance.

The Effectiveness of the Buccal Myomucosal Flap on Speech and Surgical Outcomes in Cleft Palate: A Systematic Review

Purpose: A systematic review was conducted to assess speech and velopharyngeal competence outcomes following the buccal myomucosal flap surgical approach used for primary palatoplasty and secondary surgery for velopharyngeal insufficiency (VPI) in individuals with cleft palate. Methods: A systematic review was guided by the PRISMA guidelines. Articles were included if the patients received the surgical technique for primary cleft palate repair or secondary surgery for VPI and if the study provided detailed methods on the perceptual speech assessment or visualization of postoperative velopharyngeal anatomy. Results: A total of 1013 patients were included from 11 studies. Post-surgery, normal resonance was achieved in 77.4% of patients and no nasal air emission was reported in 54.7% of patients. An improvement in velopharyngeal closure was reported in 81.8% of patients. A variety of perceptual speech assessment scales and methods for assessing velopharyngeal competence were used in the studies. Conclusions: The review suggests that the buccal myomucosal flap procedure results in improved velopharyngeal closure as evidenced by physiologic observation and reported perceptual changes in speech intelligibility, resonance balance, and reduced nasal air emission. The development of an international, standardized method for assessing and reporting speech outcomes and velopharyngeal competency is recommended to ensure accurate comparisons between surgical techniques. Keywords: Buccal flap, systematic review, perceptual speech assessment, speech outcomes, surgical outcomes. Read more →

인공와우 이식 시기에 따른 한국 청각장애아동의 말소리 명료도 변화

인공와우 이식 시기에 따른 한국 청각장애아동의 말소리 명료도 변화

Longitudinal Change in Speech Rate and Intelligibility Between 5 and 7 Years in Children With Cerebral Palsy.

Purpose We examined growth between 5 and 7 years in speech intelligibility, speech rate, and intelligible words per minute (IWPM) in 3 groups of children: those who were typically developing (TD), those with cerebral palsy (CP) and clinical speech motor impairment (SMI), and those with CP and no SMI (NSMI). Method Twenty-six children with CP, 16 with SMI, and 10 with NSMI were each seen at 5, 6, and 7 years of age. A cross-sectional group of 30 age-matched TD children, 10 in each age group, were included as controls. All children produced a corpus of utterances of 2-7 words. Results All groups of children showed increases in intelligibility and IWPM between 5 and 7 years. Only children with SMI showed increases in speech rate over time. Patterns of change were similar for children in the TD and NSMI groups but different for children in the SMI group. Conclusions The window of time between 5 and 7 years is an important period of growth for the production of connected speech where nearly all children, regardless of group, made significant changes in speech intelligibility and IWPM. Interventions focusing specifically on enhancing intelligibility in this age range may help facilitate even further growth in children with SMI, who still had marked intelligibility reductions at 7 years of age.

Auditory-Perceptual Evaluation of Deep Brain Stimulation on Voice and Speech in Patients With Dystonia

To determine the effects of globus pallidus interna (GPi) deep brain stimulation (DBS) on speech and voice quality of patients with primary, medically refractory dystonia. Voices of 14 patients aged ≥18 years (males = 7 and females = 7) with primary dystonia (DYT1 gene mutation dystonia = 4, cervical dystonia = 6, and generalized dystonia = 4) with bilateral GPi DBS were assessed. Five blinded raters (two fellowship-trained laryngologists and three speech/language pathologists) evaluated audio recordings of each patient pre- and post-DBS. Perceptual voice quality was rated using the Grade, Roughness, Breathiness, Asthenia, and Strain scale and changes in speech intelligibility were assessed with the Clinical Global Impression scale of Severity instrument. Inter-rater and intrarater reliability rates for perceptual voice ratings were assessed using the kappa coefficient. Voice quality parameters showed mean improvements in Grade (P < 0.0001), Roughness (P = 0.0043), and Strain (P < 0.0001) 12 months post-DBS. Asthenia increased from baseline to 6 months (P = 0.0022) and declined significantly from 6 to 12 months (P = 0.0170). Breathiness did not change significantly over time. Speech intelligibility also improved from 6 to 12 months (P = 0.0202) and from pre-DBS to 12 months post-DBS (P = 0.0022). Grade and Strain ratings had nearly perfect and substantial inter-rater agreement (0.84 and 0.71, respectively). Voice and speech intelligibility improved after bilateral GPi DBS for dystonia. GPi DBS may emerge as a potential treatment option for patients with medically refractory laryngeal dystonia.

Introducing the Beatalk technique: using beatbox sounds and rhythms to improve speech characteristics of adults with intellectual disability.

Individuals with intellectual disability (ID) often demonstrate speech impairments and reduced intelligibility. However, traditional treatment methods, which involve using repetitive verbal and non-verbal exercises, may not be fully suitable for this population. As adults with ID tend to lose interest and motivation facing the demands of a typical speech therapy session, other intervention methods are needed. The current study tested a novel intervention technique, Beatalk, based on practising vocally produced sounds and rhythms, imitating the sounds produced by rhythm machines in an a cappella musical context (i.e., human beatboxing). Human beatboxing may be a particularly effective tool since it involves intense production of speech sounds (phonemes) that can be misarticulated in the presence of speech disorders; it is relatively easy to learn and practice, and is also considered 'fun'. As many of the features of beatboxing make it a promising method for speech therapy, this pioneering study aimed to examine its effectiveness in comparison with a traditional speech therapy. Twelve adults with moderate ID and low speech intelligibility (age 24-48 years) participated in a speech therapy group for 6 weeks. Six participants were assigned to the Beatalk (study) group and six to a traditional (control) therapy group. Pre- to post-treatment changes in speech intelligibility and voice measures were assessed. The preliminary data demonstrate that both types of therapy groups resulted in improved performance in articulation accuracy and voice measures, yet the Beatalk technique yielded larger gains. The results present initial evidence for the beneficial effect of the Beatalk technique as an intervention tool for adults with ID. It is an easy-to-use technique in the context of speech therapy, and may enhance verbal communication skills in this population.

Treating Speech Movement Hypokinesia in Parkinson's Disease: Does Movement Size Matter?

This study evaluates the effects of a novel speech therapy program that uses a verbal cue and gamified augmented visual feedback regarding tongue movements to address articulatory hypokinesia during speech in individuals with Parkinson's disease (PD). Five participants with PD participated in an ABA single-subject design study. The treatment aimed to increase tongue movement size using a combination of a verbal cue and augmented visual feedback and was conducted in 10 45-min sessions over 5 weeks. The presence of visual feedback was manipulated during treatment. Articulatory working space of the tongue was the primary outcome measure and was examined during treatment and in cued and uncued sentences pre- and posttreatment. Changes in speech intelligibility in response to a verbal cue pre- and posttreatment were also examined. During treatment, 4/5 participants showed a beneficial effect of visual feedback on tongue articulatory working space. At the end of the treatment, they used larger tongue movements when cued, relative to their pretreatment performance. None of the participants, however, generalized the effect to the uncued sentences. Speech intelligibility of cued sentences was judged as superior posttreatment only in a single participant. This study demonstrated that using an augmented visual feedback approach is beneficial, beyond a verbal cue alone, in addressing articulatory hypokinesia in individuals with PD. An optimal degree of articulatory expansion might, however, be required to elicit a speech intelligibility benefit.

Causal cortical dynamics of a predictive enhancement of speech intelligibility

Speech perception may be underpinned by a hierarchical cortical system, which attempts to match “external” incoming sensory inputs with “internal” top-down predictions. Prior knowledge modulates internal predictions of an upcoming stimulus and exerts its effects in temporal and inferior frontal cortex. Here, we used source-space magnetoencephalography (MEG) to study the spatiotemporal dynamics underpinning the integration of prior knowledge in the speech processing network. Prior knowledge was manipulated to i) increase the perceived intelligibility of speech sentences, and ii) dissociate the perceptual effects of changes in speech intelligibility from acoustical differences in speech stimuli. Cortical entrainment to the speech temporal envelope, which accounts for neural activity specifically related to sensory information, was affected by prior knowledge: This effect emerged early (∼50 ms) in left inferior frontal gyrus (IFG) and then (∼100 ms) in Heschl's gyrus (HG), and was sustained until latencies of ∼250 ms. Directed transfer function (DTF) measures were used for estimating direct Granger causal relations between locations of interest. In line with the cortical entrainment result, this analysis indicated that prior knowledge enhanced top-down connections from left IFG to all the left temporal areas of interest – namely HG, superior temporal sulcus (STS), and middle temporal gyrus (MTG). In addition, intelligible speech increased top-down information flow between left STS and left HG, and increased bottom-up flow in higher-order temporal cortex, specifically between STS and MTG. These results are compatible with theories that explain this mechanism as a result of both ascending and descending cortical interactions, such as predictive coding. Altogether, this study provides a detailed view of how, where and when prior knowledge influences continuous speech perception.

Long-term Outcome of Speech Intelligibility in Maxillary Dental Rehabilitation with Full Dentures: A Prospective Study Using Automatic Speech Quantification.

Complete maxillary edentulism and prosthetic rehabilitation with removable full dentures are known to affect speech intelligibility. The aim of this study was to prospectively investigate the long-term effect of time on speech intelligibility in patients being rehabilitated with newly fabricated full maxillary dentures. Speech was recorded in a group of 14 patients (male = 9, female = 5; mean age ± standard deviation [SD] = 66.14 ± 7.03 years) five times within a mean period of 4 years (mean ± SD: 47.50 ± 18.16 months; minimum/maximum: 24/68 months) and in a control group of 40 persons with healthy dentition (male = 30, female = 10; mean age ± SD = 59 ± 12 years). All 14 participants had their inadequate removable full maxillary dentures replaced with newly fabricated dentures. Speech intelligibility was measured by means of a polyphone-based speech recognition system that automatically computed the percentage of accurately spoken words (word accuracy [WA]) at five different points in time: 1 week prior to prosthetic maxillary rehabilitation (both with and without inadequate dentures in situ) and at 1 week, 6 months, and a mean of 48 months after the insertion of newly fabricated full maxillary dentures. Speech intelligibility of the patients significantly improved after 6 months of adaptation to the new removable full maxillary dentures (WA = 66.93% ± 9.21%) compared to inadequate dentures in situ (WA = 60.12% ± 10.48%). After this period, no further significant change in speech intelligibility was observed. After 1 week of adaptation, speech intelligibility of the rehabilitated patients aligned with that of the control group (WA = 69.79% ± 10.60%) and remained at this level during the examination period of 48 months. The provision of new removable full maxillary dentures can improve speech intelligibility to the level of a healthy control group on a long-term basis.

Sound system analysis and design of the Minnesota State House

During the renovations of the Minnesota Capitol we were called to advise on the sound system of the House of Representatives. In order to assess the quality of the current system we performed noise, RT and STI measurements. Using the collected information we created an EASE model for the room to look at improvement proposals. This presentation addresses the differences between measured and simulated (predicted) STI values and the use of modeling tools for design. Due to the type of client we had for this project (final user, political) we were asked to report findings and recommendations in a presentation format and relied on auralizations as a tool for demonstrating changes in speech intelligibility between the existing and proposed sound systems.

The role of phase-locking to the temporal envelope of speech in auditory perception and speech intelligibility.

The temporal envelope of speech is important for speech intelligibility. Entrainment of cortical oscillations to the speech temporal envelope is a putative mechanism underlying speech intelligibility. Here we used magnetoencephalography (MEG) to test the hypothesis that phase-locking to the speech temporal envelope is enhanced for intelligible compared with unintelligible speech sentences. Perceptual "pop-out" was used to change the percept of physically identical tone-vocoded speech sentences from unintelligible to intelligible. The use of pop-out dissociates changes in phase-locking to the speech temporal envelope arising from acoustical differences between un/intelligible speech from changes in speech intelligibility itself. Novel and bespoke whole-head beamforming analyses, based on significant cross-correlation between the temporal envelopes of the speech stimuli and phase-locked neural activity, were used to localize neural sources that track the speech temporal envelope of both intelligible and unintelligible speech. Location-of-interest analyses were carried out in a priori defined locations to measure the representation of the speech temporal envelope for both un/intelligible speech in both the time domain (cross-correlation) and frequency domain (coherence). Whole-brain beamforming analyses identified neural sources phase-locked to the temporal envelopes of both unintelligible and intelligible speech sentences. Crucially there was no difference in phase-locking to the temporal envelope of speech in the pop-out condition in either the whole-brain or location-of-interest analyses, demonstrating that phase-locking to the speech temporal envelope is not enhanced by linguistic information.

Speech intelligibility can improve rapidly during exposure to a novel acoustic environment

In natural listening environments, the background noises and the acoustic spaces they occupy can vary greatly, both in their characteristics and in their impact on speech intelligibility. It has been suggested that listeners build up a statistical representation of ongoing noises; however, listeners can move around a room or move from one room to another, constantly changing both the background noises and the reverberation around them. If listeners are to make use of such statistics to aid in speech intelligibility, they must engage in a constant adaptation. We asked normal and hearing-impaired listeners to identify in real-time a stream of random target words in a contiguous series of novel acoustic environments lasting 13 s each, thus measuring the extent and time-course of changes in speech intelligibility that listeners experience in a new environment. The results from our task demonstrate that most listeners experience a rapid increase in speech intelligibility over several seconds of exposure to certain acoustic environments, but not to others. This suggests that there are classes or types of noises and reverberations that can be adapted to over a short time course and others that cannot. [Work supported by the MRC and the CSO.]

A Preliminary Investigation of Longitudinal Changes in Speech Production over 18 Months in Young Children with Cerebral Palsy

Objective: This study examined longitudinal change in speech intelligibility, vowel space, and word duration over 18 months among children with cerebral palsy (CP) who varied in the severity of their speech motor involvement. The study also examined relationships among variables at each time point. Method: Twenty-two children with CP participated in the study (mean age = 50 months at the first time point). Speech samples were collected at four time points that were 6 months apart. Children were separated into four severity groups based on intelligibility scores. Results: Change over time varied by severity. Children with CP who did not have speech motor involvement and children in the mild group showed gains in intelligibility, but no changes in vowel space area or word duration. Children in the moderate group showed no significant change, and children in the severe group showed increased vowel space and decreased word durations. Significant positive correlations between intelligibility and vowel space were noted at each time point for data pooled across all children. Conclusion: Children showed different patterns of change over time in intelligibility, vowel space, and word duration based on their speech motor abilities. The relationship between intelligibility and vowel space across severity groups was constant, suggesting a robust relationship between these variables.

Use of high-rate envelope speech cues and their perceptually relevant dynamic range for the hearing impaired

The ability of hearing-impaired (HI) listeners to use high-rate envelope information in a competing-talker situation was assessed. In experiment 1, signals were tone vocoded and the cutoff frequency (f(c)) of the envelope extraction filter was either 50 Hz (E filter) or 200 Hz (P filter). The channels for which the P or E filter was used were varied. Intelligibility was higher with the P filter regardless of whether it was used for low or high center frequencies. Performance was best when the P filter was used for all channels. Experiment 2 explored the dynamic range over which HI listeners made use of high-rate cues. In each channel of a vocoder, the envelope extracted using f(c) = 16 Hz was replaced by the envelope extracted using f(c) = 300 Hz, either at the peaks or valleys, with a parametrically varied "switching threshold." For a target-to-background ratio of +5 dB, changes in speech intelligibility occurred mainly when the switching threshold was between -8 and +8 dB relative to the channel root-mean-square level. This range is similar in width to, but about 3 dB higher in absolute level than, that found for normal-hearing listeners, despite the reduced dynamic range of the HI listeners.